Movable coil for electrodynamic receivers



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E. S. PRIDHAM ET AL.

MovABLE COIL FOR ELECTRODYNAMIC REGEIVERS FiledAlVIay l0, 1922 lllPatent dan., 13, 1925,

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EDWIN S. PRIDHAM AND PETER L. I'IilIiTSEIhL` OF OAKLAND, CALIFORNIA,ASSIGNORS T0 THE M AGNAVOX COMPANY, OF OAKLAND, CALIFORNIA, ACORPORATION OF ARIZONA.

MOVABLE COIL FOR ELECTRODYNAMIC RECEIVE-RS.

AppIication led May 10,

Z 1o all whom it may concern:

Be it known that we, EDWIN IDRIDHAM and PETER L. JENSEN, citizens of theUnited States, residing at Oakland, county of Alameda, and State ofCalifornia, have invente-d new and useful Improvements in Movable Coilsfor Electrodynamic Receivers, of which the following is a specification.

This invention relates to movable coils for electro-dynamic receivers,

.il receiver of the type under consideration is illustrated anddescribed in our application, Serial .No 377,354, filed April 28th,1920, of which the present application .is a continuation andimprovement.

The receiver comprises generally an electro-magnet havingconcentric polepieces with a circular coil disposed in the annular space between thepole pieces, said coil bcing rigidly attached to the diaphragm of asound box. The object of the present. inventionis to simplify andimprove the construction, operation and assembly of a movable coil ofthis type.

One form which our invention may assume ,is exemplified in the followingdescription and illustrated in the accompanying drawing, in Which- Thefigure' shows a central sectional View of the upper portion of afreceiver embodying our invention'.

So much of the magnetic structure asis necessary to an understanding ofthe invention is shown herein and `includes an iron casing 10, a core 11Within the casing and a winding 12 for the core. The core terminates ina pole piece 13 and a plate Mfitted upon the casing and provided with acircular opening to surround the pole piece 13 constitutes an outer polepiece. These. pole pieces should be carefully spaced so as to leave atrue annular space for the reception of the movable coil.

This coil comprises a ring-shaped frame 15 of insulating material formedwith a depression 16 to receive a winding 17. This winding consists of alarge number of turns of very fine Wire, 'The coil is rigidly connectedto a diaphragm 18 of a sound box by means` of abracket 19. This bracketis somewhat cone-shaped' in form With its sides cut away, vleaving threeor more legs 20. The legs each have a small integral lug.

1922. Serial No. 559,751.

2l at their lower ends to enter a small opening 22 in the insulatingframe of the coil for connecting the parts together. The apex or topportion 23 of the bracket is provided with a central openingl throughwhich a ssrew 24 passes for connecting the saine to the diaphragm, thescrew lbeing preferably provided with a nut 25.

Since the coil vibrates freely, it is important to bring the leads intothe coil in such a way as to avoid breakage and this we accomplish byconnecting the ends of the coil b v soldering or otherwise to flatmetallic conducting strips 26, which are led along the legs of thebracketand across the lower face of the diaphragm to the outer edgethereof, where they connect with binding posts 27. The metallic stripsare laid between twov adhesive tapes 28 and by means -of theseadhesivetapes the conducting strips are held in place on the bracket anddiaphragm. Inasmuch as the vibration at the periphery of the diaphragmis comparatively small, the conducting strips are not subjected to theliability of breakage as they would be if they extended directly outfrom the movable coil to the stationary posts. 1

In assembling the coil, the bracket is connected to the frame thereof byslightly compressing the legs to bring them within the frame so thatthelugs 21 enter the openings in the frame. Then the legs are spread andthe lugs bent over to retain the parts together. The bracket isthereafter connected to the diaphragm and the latter is positioned onthe sound box to bring the movable coil into proper' position Within theannular space bet-Ween the poles. IVe nd that a bracket, such as shownherein, having a somewhat conical shape affords the desired rigidityand, furthermore, the open sides are important, since an enclosedconnecting member or bracket in this location would impair the value ofthe tones given oft' by the diaphragm.

Having thus described our invention, what We claim and desire to secureby Letters Patent is:

1. In an electro-dynamic receiver, an inner cylindrical pole piece, anouter pole piece having a cylindrical opening surrounding `and spacedfrom the innepole 1.iece, a circular coil positioned within .irannularlli) space between the pole pieces, said coil comprising an insulatingframe having a large number' ot' turns oi' line Wire Wound upon itsexterior, a flexible diaphragm and means for rigidly connecting saidframe to the diaphragm, saidl connecting means comprising a conicalmember cut away at its sides to form legs, said legs fitting within theframe and each having an integral lug to enteran opening in the frameand means for connecting the apex of the bracket to the central portionoi' the diaphragm.

2. In an electro-dynamic receiver, an inner cylindrical pole piece, anouter pole piece having a circular opening surrounding and spaced fromthe inner pole piece, a circular coil positioned Within the annularspace between the polepieces, said coil comprising an insulating framehaving a large number of turns of fine Wire Wound upon its exterior, adiaphragm, abracl'ret having a plurality of legs extending from theinsulating Jframe up to the diaphragm for rigidly connecting the coilthereto, and means for electrically connecting thecoil to the stationarybinding posts comprising conducting strips ad?.

hesively secured to the legs of the bracket and to the under surface ofthe diaphragm.

3. In an electro-dynamic receiver, an inner cylindrical pole piece,having a circular opening surrounding and spaced from the inner polepiece, a circulaicoil positioned Within the annular space bef. tween thepole pieces, said coil comprising an insulating frame having a largenumber of turns ot' ine Wire Wound upon its eX- terior, a diaphragm, abracket having a plurality of legs extending from, the insulating frameup to the diaphragm for rigidly connecting the coil thereto, and meansfor elec trically connecting the coil to the stationary binding posts,said means comprising a pair of adhesive strips for each end of the coilapplied to the legs of the bracket and. to the under side of thediaphragm and a conductpr carried between each pair of adhesive strips.

lEDWiN s. PEIDHAM. PETER L. JENSEN.

an outer pole piece

